Amateur Extra: Blocking Dynamic Range

Today’s question for you studying to be Extra’s is a real doozy, about receivers. [E4D01]

What is meant by the blocking dynamic range of a receiver?

A. The difference in dB between the noise floor and the level of an incoming signal which will cause 1 dB of gain compression
B. The minimum difference in dB between the levels of two FM signals which will cause one signal to block the other
C. The difference in dB between the noise floor and the third order intercept point
D. The minimum difference in dB between two signals which produce third order intermodulation products greater than the noise floor

Whoa, man. Lots of big words to digest in that one. First off, just what in the heck do we mean by “Blocking Dynamic Range?”

Blocking Dynamic Range (BDR) indicates how well the receiver handles strong nearby
signals before desensitization occurs. By definition (or, something you unfortunately have to memorize!) its the value of an input signal, relative to the MDS (or Minimum Discernable Signal, also called the noise floor) of the receiver, that will cause the gain to decrease by 1dB.

For example, if a – 25 dBm input signal causes 1 dB of gain compression for a receiver with a
MDS of -135 dBm, the blocking dynamic range is 110 dB.

Therefore, the correct answer is: A. The difference in dB between the noise floor and the level of an incoming signal which will cause 1 dB of gain compression.

Questions like these are what makes the Amateur Extra exam just that much more challenging, when you have to memorize definitions such as this!